Polymers contact lenses

Vinyl CH2=CH-0-C-CI II 0 5130-24-5 89-90/ 760 Polymers Contact lenses Pharmaceuticals N-dealkylation... 

OEA-based composites are used for the production of electrical insulation, elastic concretes, and abrasive materials and for some medical purposes [131]. By means of OEA, copolymers can be produced that provide hydrophilic membranes permeable to urea and water, some biologically active polymers, contact lenses, and other medical materials [132-135]. 

Synthetic gels Organic polymer, contact lenses, high water absorbent resins, siUca gels... 

Patent Number US 5520910 A 19960528 ANTIMICROBIAL POLYMER, CONTACT LENS AND CONTACT LENS-CARE ARTICLES... 

K. Hashimoto, Y. Inaba, S. Shimura, T. Mogami, T. Kojima, and Y. Ushiyama, Antimicrobial polymer, contact lens and contact lens-care articles, US Patent 5 520 910, assigned to Nippon Chemical Industrial (Tokyo, JP) Seiko Epson Corporation (Tokyo, JP), May 28,1996. 

Not every polymer can be manufactured successfully into a contact lens. Several important properties for both ocular physiology and patient handling are required of a material for a contact lens appHcation (1,11). In addition, the type of lens appHcation, ie, rigid, flexible, or soft, will dictate the range and importance of the key properties. 

Water content indirectly affects other lens characteristics. Water evaporation from the lens can result in a dry eye sensation and subsequent desiccative erosion of the cornea. Clinical studies have shown the incidence of corneal erosion as a result of lens desiccation to be a material-dependent and water-content-dependent phenomenon (25,26). The nature of water and sodium ions in hydrogels has been studied primarily by nmr and thermal techniques (27,28). An empirical relationship between water mobility in contact lens polymers and desiccative staining has been proposed (29). 

A recent addition to Table 3, Reactive Blue 246 differs from the other dyes and is not added to a finished lens. The dye molecule has methacrylate groups attached to an anthraquinone and is incorporated directiy into the polymer matrix during polymer cure (175). This in-monomer concept has the potential to reduce dramatically the cost of visibiUty tinting of a contact lens. 

Table 5 Commonly Used Monomers, Comonomers, and Cross-Linkers in Contact Lens Polymers... 

Hard contact lenses are composed of a polymer that repels water because the constituent repeating units (the monomers that link together to form the polymer) are nonpolar, hydrophobic segments. The first hard contact lens was constructed in 1948 from the monomer known as methyl methacrylate (MMA), yielding the polymer poly(methyl methacrylate) or PMMA. This material offers durability, optical transparency, and acceptable wettability for optimal comfort. Today the rigid lens material of hard contact lenses is often constructed by combining MMA with one or more additional hydrophobic monomers to provide better gas permeability. 

Contact Lens Material. Dr. Jay F. Kunzler and Dr. Joseph A. McGee, Department of Polymer Chemistry, Bausch Lomb, Chemistry Industry 21 (1995), 615. 

Goda T, Ishihara K (2006) Soft contact lens biomaterials from bioinspired phospholipid polymers. Expert Rev Med Devices 3 167-174... 

P.C. Nicolson, J. Vogt, Soft contact lens polymers An evolution, Biomaterials 22 (2001) 3273-3283. 

Contact lens fluid -polyethylene oxide) m [POLYETHERS - ETHYLENE OXIDE POLYMERS] (Vol 19)... 

Polysiloxanes (silicones) are one of the most studied classes of polymers. They exhibit a variety of useful properties not common to non-metal-contain-ing macromolecules. They are characterized by combinations of chemical, mechanical, electrical, and other properties that, when taken together, are not found in any other commercially available class of materials. The initial footprints on the moon were made by polysiloxanes. Polysiloxanes are currently sold as high-performance caulks, lubricants, antifoaming agents, window gaskets, O-rings, contact lens, and numerous and variable human biological implants and prosthetics, to mention just a few of their applications. 

However, it should be imderstood that many recently developed contact lens materials contain polymers that block the transmission of light in the ultraviolet region. Therefore when an ultraviolet light source, such as a... 

While the silicone polymer phase provides a high enough oxygen permeability, it also dominates the surface characteristics, i.e., the surface of silicone hydrogel is too hydrophobic to be used as a contact lens. The silicone phase also readily absorbs... 

The three key features of LCVD coating ideally suited for biomaterial surface, and the important balance between the bulk properties and the surface properties, could be best illustrated by examples of nanofilms of methane plasma polymer on a contact lens made of polydimethylsiloxane elastomer. Hence, some details of processing factors and their influence on the overall properties of the product are described in the following sections. 

Liquid water on one side of a silicone contact lens permeates through the lens by a solution-diffusion mechanism and evaporates on the other side quickly according to the permeability of water, whereas the solubility of water in silicone polymer is low [1]. The high water vapor permeability was speculated to be one of the reasons causing the suction cup effect that makes the lens stationary on one spot and tenaciously stick to the cornea this may damage the corneal epithelium and result in other complications. However, the high permeability per se cannot be the reason for the suction cup effect if the exterior surface is covered by the tear film, i.e., if there is no driving force for water permeation. 

The hydrophobicity of the surface prevents the wetting by tear and tends to expose dry surface of a contact lens. Therefore, rapid dehydration of the corneal tissues could occur, which could cause the damage of corneal epithelium. However, this explanation seems to be oversimplified in light of the adsorption of protein, which makes a hydrophobic surface wettable by tear fluid, as described in Chapter 26. Moreover, the highly hydrophobic surface characteristic of silicone rubber tends to encourage the deposition of protein and mucus of the tear on the surface of the lens. Lipids and lipid-soluble materials follow the same track and eventually penetrate into the bulk phase of the contact lens. Because of these undesirable factors, the use of silicone contact lenses of various chemical compositions and with surface treatments has not been successful but rather disastrous because of the interfacial characteristics of silicone contact lens on the cornea, which cannot be oflfset by these efforts. It indicates that more profound surface modification to cope with the problems rather than mere surface treatment is needed in capitalizing on the advantageous bulk properties of silicone polymers. 

The effects of the composite parameter WjFM on the friction coefficient of the contact lens coated by methane plasma polymer at a fixed coating thickness 31.2nm are shown in Figure 35.3. The friction coefficient, which is the tangential force divided by the normal force, was calculated from the sliding angle of a contact lens placed on a glass plate that was coated with plasma polymer of tetrafluoroethylene (TFE). The friction coefficient of the methane plasma polymerized contact lens is independent of WjFM in the range 2.6-29.1 GJ/kg. 

Contact lenses are coated with an approximately 20-nm-thick layer of a methane-based plasma polymer by a continuous mode operation, which is shown schematically in Figure 36.2. The total processing time for a contact lens is approximately 40 min, which includes drying wet contact lenses before plasma polymerization coating, evacuation, LCVD, and repressurizing for sample removal. The coating operation could be continuous for approximately 30 days between maintenance breaks. The reactor is capable of coating 30 million contact lenses a year (340 days of operation). 

Many other applications for plasma polymers in the Life Sciences have been dted, often in relation to implantable medical devices or materials, with the goal of concealing the device from the bodies defence mechanisms, or improving cell colonisation of the material, e.g. endothelial cell growth into vascular grafts. A number of excellent studies from the group of Hans Griesser (CSIRO, Australia) describe the use of plasma polymers as substrates to which biomolecules can be immobilised. These immobilisations have been demonstrated to enhance the medium-term acceptability of contact lens materials and may prove relevant to implantable devices. 

Hydroxyethyl cellulose is a nonionic, water-soluble polymer widely used in pharmaceutical formulations. It is primarily used as a thickening agent in ophthalmic and topical formulations, although it is also used as a binder and film-coating agent for tablets. It is present in lubricant preparations for dry eye, contact lens care, and dry mouth. ... 

Fig. 3 Structures of some polymers used in contact lens formulations (A) a typical poly siloxane and (B) a typical polyperfluoroether.

Nicolson, P.C. Vogt, J. Soft contact lens polymers an evolution. Biomaterials 2001, 22, 3273-3283. 

In humans, a contact lens lies in the conjunctival sac of the eye. In a closed eye, this sac is a slitlike space between the conjunctiva-covered eyeball and the eyelids. Contact lenses are small polymer bowls that float on tears superficial to the corneal eye layer and correct existing visual deficiencies similarly to glasses. While the idea of the contact lens was formulated as early as 1508, it was not until the 1800s that contact lenses became a reality. Hard plastic contact lenses were invented around 1936, and although soft lenses were invented in 1960, they were not available on the commercial market until 1971. 

---